1. Field of the Invention
The present invention relates to methods for making semiconductor devices, and in particular, to a method for making a semiconductor device including a step for forming a silicon oxide insulating film containing fluorine with a low dielectric constant.
2. Description of the Related Art
With progress toward higher integration density in semiconductor device fields such as LSIs, the width of an interlayer insulating film between two adjacent wiring sections formed on a wiring layer in a multilayer wiring configuration has decreased and the thickness of the interlayer insulating film between two wiring layers has also decreased. Such decreases between wiring sections result in increased inter-wiring capacitance. Thus, effective operation speeds of semiconductor devices deviate from the 1/K scaling rule and therefore advantages in a high integration density are offset, wherein K indicates reduction rate. Prevention of increased inter-wiring capacitance is an essential technology to be solved in order to achieve high speed operation of high-integration density semiconductor devices, low electric power consumption, and less heat formation.
Use of a low dielectric material for the interlayer insulating film is effective in decreasing the inter-wiring capacitance of a high integration density semiconductor device as disclosed in, for example, Japanese Unexamined Patent Publication No. 63-7,650. Typical examples of such low dielectric materials include inorganic materials such as a silicon oxide insulating film containing fluorine (hereinafter referred to as SiOF insulating film). Other materials include organo-polymeric materials, such as organic SOG (Spin On Glass) containing siloxane, polyimides, polyparaxylene (commercial name: Parylene, made by Parylene Conformal Coating System, Inc.) and polynaphthalene; and fluorine resins, such as FLARE (commercial name, made by AlliedSignal Inc.), perfluoro polyimides, and poly(fluoroallyl ether). These low dielectric materials are introduced in, for example, page 105 of "Nikkei Microdevice" (issued in July, 1995).
Japanese Unexamined Patent Publication No. 7-3,727 by the applicant of the present invention discloses a monolithic insulating film, which can be used for a semiconductor device having interlayer insulation films with a low dielectric constant and high reliability. That is, a low dielectric material having a relative dielectric constant of no greater than 3.5 is used for adjacent wiring sections and different wiring layers, and each low dielectric material layer is intercalated with insulating films having excellent film characteristics, such as SiO.sub.2 (relative dielectric constant: 4) and Si.sub.3 N.sub.4 (relative dielectric constant: 4 to 6).
Among low dielectric materials, SiOFs can be produced by the same film making process as a conventional inorganic interlayer insulating film and thus using any current production apparatuses. In detail, SiOFs are formed by a process disclosed in Japanese Unexamined Patent Publication No. 6-333,919, in which a fluorosilane gas such as SiF.sub.4 is used instead of a material gas for forming the silicon oxide insulating film, such as SiH.sub.4, and Si--F bonds are incorporated in the silicon oxide insulating film by CVD. Since SiH.sub.4 has a low dissociation rate in plasma, a suitable amount of Si--F bonds are barely incorporated in the silicon-oxide insulating film.
Japanese Unexamined Patent Publication No. 6-295,907 by the applicant of the present invention discloses a method for promoting material gas dissociation in plasma by adding a basic gas such as NH.sub.3. Although this method noticeably decreases the hydroxyl group content in the silicon oxide insulating film, it is less effective in decreasing the relative dielectric constant.
As disclosed in Japanese Unexamined Patent Publication No. 7-90,589, use of fluorocarbon gas, e.g. CF.sub.4 and C.sub.2 F.sub.6, as a fluorine atom source decreases the relative dielectric constant, whereas the possibility of contamination due to incorporation of carbon atoms still remains.